Stainless Steel Filler Metals

What it is

Stainless filler metals come in three main forms. Stick electrodes are classified under AWS A5.4, for example E308L-16. Bare wires and rods for MIG, TIG and submerged arc are under AWS A5.9, for example ER308LSi. Flux-cored wires are under AWS A5.22, for example E308LT1-1. The number (308, 309, 316 and so on) is the alloy type. The basic rule is to match the filler to the base metal, with 309L used for stainless to carbon steel and other dissimilar joints.

How to read it

• E = electrode, ER = electrode or rod, EC = composite metal-cored wire.
• L = low carbon, which limits carbide precipitation and loss of corrosion resistance near the weld.
• Si = higher silicon for better wetting and bead shape in MIG.
• H = controlled higher carbon for high-temperature strength.
• Stick suffixes: -15 for DCEP only, -16 for AC or DCEP, -17 a variant of -16 with a different slag and bead profile.
• Flux-cored: T0 or T1 shows position (flat and horizontal, or all position), and the final digit shows the gas, such as -1 for CO2 and -4 for argon-CO2 mix.

The three workhorse fillers

Key points

• Use 316L, not 308L, on 316 where corrosion resistance matters.
• Use 309L for stainless to mild steel. Using 308L on that joint can crack or lose corrosion resistance.
• TIG and MIG on stainless use argon-based gases. Many MIG stainless wires call for tri-mix or argon with a small amount of CO2 or oxygen. Follow the wire maker's chart.
• Back purge tube and pipe roots with argon to protect the inside surface.
• Keep stainless fillers clean, capped and away from carbon steel dust.
• On code and corrosion-critical work, the WPS sets the filler, ferrite control and testing.

Common mistakes

• Stocking only 308L and using it on everything stainless.
• Selling a stainless TIG rod for a MIG spool gun job, or the reverse.
• Running 75/25 argon-CO2 on stainless solid-wire MIG. (Flux-cored -4 wires are the exception and are made for 75-80% argon-CO2.)
• Ignoring the stick electrode suffix and running a -15 rod on AC.

Governing standards: AWS A5.4 (stainless steel stick electrodes); AWS A5.9 (bare stainless wires and rods); AWS A5.22 (stainless flux-cored and metal-cored electrodes and rods).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.